Baghdad: A suicide bomber on a bicycle killed at least 28 people and wounded 20 others on Monday when he blew himself up inside a police base in Baquba, police said.

They said the bomber struck during a training session at the base in Baquba and blew himself up amidst members of a rapid reaction force, said Major General Ghanim Al Quraishi.

A shopkeeper whose store is close to the base said he had seen a man riding a bicycle slip through a gap in the wall surrounding the compound and heard a huge blast seconds later.

"I saw many bodies covered in blood. Some were dying, some had arms and legs blown off," said store owner Ali Shahine.

Baquba is the capital of Diyala province, where Al Qaida and other Sunni Islamist militants as well as Shiite Muslim militias operate. The US military launched a major offensive against Al Qaida in Baquba this year.